Gold-Catalyzed Formal [4+2] Cycloaddition of 5-(Ethynylamino)pent-2-yn-1-yl Esters to 1,2,3,5-Tetrahydrobenzo[g]quinolines

A synthetic method to prepare 1,2,3,5-tetrahydrobenzo[g]quinolines efficiently that relies on gold-(I)-catalyzed cycloisomerization of 5-(ethynylamino)pent-2-yn-l-yl esters at room temperature under atmospheric conditions is described. The proposed reaction mechanism presents a unique instance of an in situ formed allenic ester and gold keteniminium species to undergo a formal [4 + 2] cycloaddition pathway.